Implantable stimulation devices are devices that generate and deliver electrical stimuli to nerves and tissues for the therapy of various biological disorders, such as pacemakers to treat cardiac arrhythmia, defibrillators to treat cardiac fibrillation, cochlear stimulators to treat deafness, retinal stimulators to treat blindness, muscle stimulators to produce coordinated limb movement, spinal cord stimulators to treat chronic pain, cortical and deep brain stimulators to treat motor and psychological disorders, and other neural stimulators to treat urinary incontinence, sleep apnea, shoulder sublaxation, etc. The description that follows will generally focus on the use of the invention within a Deep Brain Stimulation (DBS) system, such as is disclosed in U.S. patent application Ser. No. 13/741,116, filed Jan. 14, 2013. However, the present invention may find applicability in any implantable medical device system.
As shown in FIG. 1, a DBS system typically includes an Implantable Pulse Generator (IPG) 10, which includes a biocompatible device case 12 formed of titanium for example. The case 12 typically holds the circuitry and battery 14 necessary for the IPG to function, although IPGs can also be powered via external energy and without a battery. The IPG 10 is coupled to electrodes 16 via one or more electrode leads (two such leads 18 and 20 are shown), such that the electrodes 16 form an electrode array 22. The electrodes 16 are carried on a flexible body 24, which also houses the individual signal wires 26 coupled to each electrode. In the illustrated embodiment, there are eight electrodes on lead 18, labeled E1-E8, and eight electrodes on lead 20, labeled E9-E16, although the number of leads and electrodes is application specific and therefore can vary. The leads 18 and 20 couple to the IPG 10 using lead connectors 28, which are fixed in a header material 30 comprising an epoxy for example.
In a DBS application, as is useful in the treatment of Parkinson's disease for example, the IPG 10 is typically implanted under the patient's clavicle (collarbone), and the leads 18 and 20 are tunneled through the neck and between the skull and the scalp where the electrodes 16 are implanted through holes drilled in the skull in the left and right and side of the patient's brain, as shown in FIG. 2. Specifically, the electrodes 16 may be implanted in the subthalamic nucleus (STN) or the pedunculopontine nucleus (PPN). The electrodes may be implanted in both of these regions in the left and right side of the brain, meaning that four leads would be necessary, as shown in the above-referenced '116 application. Stimulation therapy provided by the IPG 10 has shown promise in reducing a patient's Parkinson's symptoms, in particular tremor that can occur in the patient's extremities.
As shown in cross section in FIG. 4, the IPG 10 typically includes an electronic substrate assembly including a printed circuit board (PCB) 34, to which various electronic components 37 are mounted; some of these components are discussed subsequently with respect to FIG. 5. Two coils (antennas) are generally present in the IPG 10: a telemetry coil 36 used to transmit/receive data to/from an external controller 50; and a charging coil 38 for charging or recharging the IPG's battery 14 using an external charger 70. The telemetry coil 36 can be mounted within the header 30 of the IPG 10 as shown, or can be located within the case 12, as shown in U.S. Patent Application Publication 2011/0112610.
FIG. 3 shows plan views of the external controller 50 and the external charger 70, and FIG. 4 shows these external devices in cross section and in relation to the IPG 10 with which they communicate. The external controller 50, such as a hand-held programmer or a clinician's programmer, is used to send data to and receive data from the IPG 10. For example, the external controller 50 can send programming data such as therapy settings to the IPG 10 to dictate the therapy the IPG 10 will provide to the patient. Also, the external controller 50 can act as a receiver of data from the IPG 10, such as various data reporting on the IPG's status. As shown in FIG. 4, the external controller 50, like the IPG 10, also contains a PCB 52 on which electronic components 54 are placed to control operation of the external controller 50; again some of these components are discussed with respect to FIG. 5. The external controller 50 is powered by a battery 56, but could also be powered by plugging it into a wall outlet for example. A telemetry coil 58 is also present in the external controller 50. A clinician's external controller is likely to only exist at a doctor's office, and not all patients having DBS implants will have patient external controllers. Alternatively, such patient external controllers may be limited in their functionality, such as merely allowing stimulation to be turned on or off.
The external controller 50 typically comprises a graphical user interface 60 similar to that used for a portable computer, cell phone, or other hand held electronic device. The graphical user interface 60 typically comprises touchable buttons 62 and a display 64, which allows the patient or clinician to operate the external controller 50 to send programs to the IPG 10 and to review any relevant status information that has been reported from the IPG 10 during its therapeutic operation.
Wireless data transfer between the IPG 10 and the external controller 50 typically takes place via magnetic inductive coupling. To implement inductive coupling functionality, both the IPG 10 and the external controller 50 have coils 36 and 58 respectively as already mentioned. Either coil can act as the transmitter or the receiver, thus allowing for two-way communication between the two devices.
Referring to FIG. 5, when data originating in the external controller's control circuitry 55 (e.g. a microcontroller) is to be sent from the external controller 50 to the IPG 10 along communication link 80, coil 58 is energized with alternating current (AC), which generates a magnetic field, which in turn induces a voltage in the IPG's telemetry coil 36. The generated magnetic field is typically modulated (51), such as by Frequency Shift Keying (FSK), which is well known in the art. The induced voltage in coil 36 can then be demodulated (11) at the IPG 10 back into the telemetered data signals, and fed to the control circuitry 15 in the IPG 10. This means of communicating by inductive coupling is transcutaneous, meaning it can occur through the patient's tissue 25.
If the communication involves adjustment to the therapy the IPG 10 is providing to the patient, the control circuitry 15 communicates relevant instructions to stimulation circuitry 27. As is known, stimulation circuitry 27 includes various current or voltage sources which can be coupled to selected electrodes 16 to provide desired therapy to the patient. Such therapy, typically referred to as a stimulation program, generally specifies various parameters for the stimulation, such as which electrodes 16 are active, whether such electrodes act as anodes (current sources) or cathodes (current sinks), and the duration, frequency, and amplitude of pulses formed at the electrodes. See, e.g., U.S. Patent Application Ser. No. 61/654,603, filed Jun. 1, 2012, for further details concerning stimulation circuitry 27.
To conserve power in the IPG 10, receiver circuitry the IPG 10 (e.g., demodulator 11) is typically only activated periodically during a short listening window to listen for communications from the external controller 50. For example, the demodulator 11 may be powered for only several milliseconds every second or so. The external controller 50 desiring to communicate with the IPG 10 will first broadcast a wake up signal recognizable by the IPG 10, which broadcast will typically continue for a long enough time to ensure that it overlaps at least one IPG listening window. Upon recognizing the wake up signal, the IPG 10 can fully power its communication circuitry, and transmit an acknowledgment signal back to the external controller 50 via modulator 13. The external controller 50 can in turn listen for this acknowledgment from the IPG 10 via its demodulator 53, which can occur after the external controller has finished broadcasting the wake up signal. Alternately, the wake up signal can contain gaps where its broadcast is temporarily suspended to listen for the acknowledgment signal. Once the acknowledgment is received and the IPG's communication circuitry fully powered, the external controller 50 can transmit its data to the IPG 10. Further details of this sort of handshaking between an external controller and an IPG can be found in U.S. Pat. No. 7,725,194, and U.S. patent application Ser. No. 13/211,741, filed Aug. 17, 2011. Typically, such communications between the external controller 50 and the IPG 10 will be predictably formatted in accordance with some protocol to ensure that communications are reliable. For example, communications may include header information, error checking data, an identification code of either or both of the transmitting and desired receiving device, etc.
The external charger 70 is used to charge (or recharge) the IPG's battery 14. Specifically, and similarly to the external controller 50, the external charger 70 contains a coil 72 which is energized via charging circuit 74 with a non-modulated AC current to create a magnetic charging field 84. This magnetic field induces a current in the charging coil 38 within the IPG 10, which current is rectified 17 to DC levels, and used to recharge the battery 14, perhaps via a charging and battery protection circuit 19 as shown. Again, inductive coupling of power in this manner occurs transcutaneously. The external charger 70 is generally held against the patient's skin or clothes and in good alignment with the IPG 10 by a belt or an adhesive patch, which allows the patient some mobility while charging. It should be noted that because of concerns of interference, the external controller 50 and external charger 70 will generally not operate at the same time, and instead one will take precedence over the other.
The IPG 10 can also communicate data back (86) to the external charger 50 using modulation circuitry 21 and switch 23, as described further in U.S. Patent Application Publication 2010/0305663. This form of communication is known as Load Shift Keying (LSK), and is useful to communicate data relevant during charging of the battery 14 in the IPG 10, such as the capacity of the battery, whether charging is complete and the external charger can cease, and other pertinent charging variables.